6.13.8 Exceptions

A common requirement in applications is to want to jump
non-locally from the depths of a computation back to, say, the
application’s main processing loop. Usually, the place that is the
target of the jump is somewhere in the calling stack of procedures that
called the procedure that wants to jump back. For example, typical
logic for a key press driven application might look something like this:

The jump back to main-loop could be achieved by returning through
the stack one procedure at a time, using the return value of each
procedure to indicate the error condition, but Guile (like most modern
programming languages) provides an additional mechanism called
exception handling that can be used to implement such jumps much
more conveniently.